Current techniques for tracking groundwater or subsurface solutions typically involve geophysical methods such as various forms of galvanic resistivity, electromagnetic conductivity, ground penetrating radar, or the drilling of many observation wells for monitoring. Other forms of tracking and monitoring rely on the measurement of magnetic fields created by electric currents flowing through underground water pathways.
A Mise-a-la-masse method has been used for directly connecting or nearly directly connecting to an ore body. In this method, resistivity or induced polarization (IP) is used as a detection mode. Ground penetrating radar can work well on very shallow targets and where there is no clay in the soil. Use of ground penetrating radar for tracking groundwater or underground solutions of any depth is limited.
Drilling is another option for identifying and/or tracking subsurface water. A drawback to drilling is that drilling does not reveal much more than what is at the location of the drill hole. To establish linkage between holes a tracer solution or some geophysical continuity test can be used. Geophysical techniques used to establish connectivity between holes may place an electrode in one hole at the horizon of interest and then lower another electrode in the second hole to see if there is a response at the horizon of interest in the second hole. This technique may establish connectivity but does not provide a surface trace of the path that the water follows between the drill holes. Confidently mapping a subsurface water system, identifying all branches of a groundwater source, or recognizing all offshoots of the water system can be difficult when limited to drilling and such geophysical methods. In addition, drilling wells is costly and can easily miss narrow streams of groundwater as it produces inconclusive data.
A method to map groundwater using electrical resistance tomography (ERT) and electro kinetic system (EKS) was developed which places many electrodes on the surface and in wells and measures all combinations of resistivity between them. The water or fluids are then caused to move using electro kinetics. Subsequently, the various resistivity combinations are re-measured. This data is combined to create a tomography picture that results from the displacement of the groundwater.
In a method using magnetism, an electric current established directly in the groundwater or aqueous system to be tracked creates a magnetic field which emanates from the ground water through which the electric current flows. The magnetic field is monitored and interpreted to elucidate the nature and location of preferential electric current flow paths following the aqueous system. At least one electrode is placed in direct contact with, or in close proximity to, the aqueous system to be investigated. If the aqueous system to be tracked has a surface expression, an electrode can be placed in the aqueous system flowing from the earth. Additional electrodes are placed in appropriate positions to provide a return path for the current. A wire used to connect the return electrode is run far outside the area of investigation to minimize the effect of the wire's electric and magnetic fields in the data. The current that is conducted through the groundwater path to the return electrode completes the circuit. The system is arranged so that the flow of current is roughly in a large loop. The magnetic field produced by the current can be measured at many locations and the measurements can be used to map the aqueous solution.
Despite the development of the various technologies listed, and others, such methods and technologies are inadequate for many useful applications. Also, ERT, EKS, IP, drilling, and so forth are limited in effectiveness when other electrical lines, magnetic fields, underground physical structures (including metal), and so forth are present. Additionally, use of such technologies in densely populated areas can be difficult.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Additional features and advantages of the technology will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the technology.